A Computational Fluid Dynamics (CFD) Analysis of an Undulatory Mechanical Fin Driven by Shape Memory Alloy

Many fishes use undulatory fin to propel themselves in the underwater environment. These locomotor mechanisms have a popular interest to many researchers. In the present study, we perform a three-dimensional unsteady computation of an undulatory mechanical fin that is driven by Shape Memory Alloy （SMA）. The objective of the computation is to investigate the fluid dynamics of force production associated with the undulatory mechanical fin. An unstructured, grid-based, unsteady Navier-Stokes solver with automatic adaptive remeshing is used to compute the unsteady flow around the fin through five complete cycles. The pressure distribution on fin surface is computed and integrated to provide fin forces which are decomposed into lift and thrust. The velocity field is also computed throughout the swimming cycle. Finally, a comparison is conducted to reveal the dynamics of force generation according to the kinematic parameters of the undulatory fin （amplitude, frequency and wavelength）.

Undulatory Theory with Paraconsistent Logic (Part I): Quantum Logical Model with Two Wave Functions

Paraconsistent logic (PL) is a non-classical logic that accepts contradiction in its foundations. It can be represented in the form of paraconsistent annotated logic with annotation of two values (PAL2v). When used to model quantum phenomena, PAL2v is called paraquantum logic (PQL). In this work, the concept of PQL is applied to create a logical model presenting the fundamental principles of quantum mechanics that support particle-wave theory. This study uses the well-known Young’s double-slit experiment, wherein quantum phenomena appear when a monochromatic light beam passes through the two slits. We focused on a reference point located between the slits, where we observed the effects of two types of wave interferences in a region defined as a two-wave region (2W region). Considering that the effect in this 2W region is very similar to that studied by Huygens, we adopt a paraquantum logical model in which a particle (or quantum) is represented by two wave functions. The two wave functions result in four State Vectors (Ket, Bra,,) in the PQL Lattice that express the symmetry and the entanglement of Quantum Mechanics. The constructed model adapts well to the quantum phenomena, is strongly consistent, and can be considered as an innovative form of analysis in the field of quantum mechanics. Based on this model, we present in two parts (Part I and Part II) the comparative analysis of values found in SchrÖdinger’s equation and probabilistic models of wave-particle theory using Bonferroni inequality.

Hydrodynamic scaling law in undulatory braking locomotion

Flow over a fish-like airfoil is numerically investigated to elaborate the hydrodynamics of the undulatory braking locomotion for an elongated eel-like body or long-based fin. For undulation with low frequency, we find that boundary layer separation occurs in a parameter region with wakes in which two vortex pairs are formed per undulatory period. The physical mechanism of separation is governed by the slip(the ratio of swimming-to-body-wave speed), and the critical value of the slip in an inertial flow regime is approximately 4/3 rather than 1, which is independent of steepness(or amplitude). The relationship between pressure drag and relative velocity(between phase speed and free stream velocity) changes from linear to quadratic, corresponding to two different flow structures;this happens due to boundary layer separation, and the piecewise scaling relationship between pressure drag and relative velocity is explicitly clarified. Considering the viscosity effects, the separation criterion and the scaling relationship in the case of an undulatory brake are both synthetically modified using the Reynolds number, with all the required parameters clearly expressed. The results of this study provide physical insight into understanding the flow structures and hydrodynamics of the undulatory braking locomotion, which has instructional significance to brake design.

Undulatory gait planning method of multi-legged robot with passive-spine

In this paper,we propose a new gait planning method for a multi-legged robot which has only 1 degree-of-freedom in each leg and has a passive body joint between two body segments.We firstly introduce the Finite State Machine(FSM)to the undulatory gait planning method of the 2n-legged robot.Then,the undulatory gait sequence for straight line motion is achieved by undulations motion.The idea that legged locomotion is achievable by less actuation of 2n-legged robot as well as the gait planning methods are verified finally by simulations and experiments.

A Novel Undulatory Propulsion Strategy for Underwater Robots

Stingrays can undulate their wide pectoral fins to thrust themselves and swim freely underwater.Many researchers have used bionics to directly imitate their undulating mechanism and manufacture undulatory underwater robots.Based on the limitations of the existing undulatory underwater robots,this paper proposes a novel undulatory propulsion strategy,which aims to use the stingray undulating mechanism more thoroughly.First,the mathematical models of both traditional and novel structures are established to accurately describe their undulating mechanism.Then,based on the dynamic mesh technology,the flow field vortex structure they generated is analyzed through fluid-structure interaction simulation,and the thrust force and lateral force generated by them are calculated,which verified that this novel propulsion strategy is indeed more effective.Finally,a prototype robot based on the improved propulsion strategy is manufactured.Compared with the existing stingray robots,the prototype has obvious advantages,thus verifying the accuracy of the simulation results.

GPS station short-term dynamic characteristics of micro displacement before Menyuan M6.4 earthquake

Continuous observation data from 24 GPS stations are selected in the area （33.0°N-41.0°N, 95.0°E-105.0°E） for this study （the period is from Jan. 1, 2015 to Jan. 20, 2016）. Three components, NS, EW and UD, of the daily solutions are filtered by the Hilbert-Huang transform （HHT） with frequency band of 5.787×10^-7-7.716 ×10^-8 Hz （20-150 days in period）. And short-term dynamic characteristics of micro displacement before Menyuan M6.4 earthquake are studied by using the temporal dependencies and cross spectrum analysis. The results show that before the earthquake the horizontal undulatory motions are higher than the average level in the series data which indicate the disturbance feature of regional stress before the earthquake. Three GPS stations on Qinghai-Tibet Plateau with their setting perpendicular to the seismogenic fault have consistent movement. The increase of amplitude of the horizontal micro motion observed before the quake is conducive to the earthquake occurrence. However, we could not be sure if the undulatory motion triggered the earthquake. It is quite necessary to build more GPS continuous observation stations and optimize the monitoring network so as to improve the understanding of the shortterm dynamic crustal variation before earthquake.

Locomotion of Gymnarchus Niloticus: Experiment and Kinematics

In addition to forward undulatory swimming, Gymnarchus niloticus can swim via undulations of the dorsal fin while the body axis remains straight; furthermore, it swims forward and backward in a similar way, which indicates that the undulation of the dorsal fin can simultaneously provide bidirectional propulsive and maneuvering forces with the help of the tail fin. A high-resolution Charge-Coupled Device （CCD） imaging camera system is used to record kinematics of steady swimming as well as maneuvering in G. niloticus. Based on experimental data, this paper discusses the kinematics （cruising speed, wave speed, cycle frequency, amplitude, lateral displacement） of forward as well as backward swimming and maneuvering. During forward swimming, the propulsive force is generated mainly by undulations of the dorsal fin while the body axis remains straight. The kinematic parameters （wave speed, wavelength, cycle frequency, amplitude） have statistically significant correlations with cruising speed. In addition, the yaw at the head is minimal during steady swimming. From experimental data, the maximal lateral displacement of head is not more than 1% of the body length, while the maximal lateral displacement of the whole body is not more than 5% of the body length. Another important feature is that G. niloticus swims backwards using an undulatory mechanism that resembles the forward undulatory swimming mechanism. In backward swimming, the increase of lateral displacement of the head is comparatively significant; the amplitude profiles of the propulsive wave along the dorsal fin are significantly different from those in forward swimming. When G. niloticus does fast maneuvering, its body is first bent into either a C shape or an S shape, then it is rapidly unwound in a travelling wave fashion. It rarely maneuvers without the help of the tail fin and body bending.

Design and Experiment on a Biomimetic Robotic Fish Inspired by Freshwater Stingray

Freshwater stingrays undulate their flexible disc-like pectoral fins to perform cruising, manoeuvring, and other motions. This undulatory propulsion has a higher propulsive efficiency and more precise manoeuvrability than most other species at low swimming velocity. In the current study, a new robotic fish inspired by the freshwater stingray was developed and tested. First, the morphology and kinematic patterns of the freshwater stingray were presented. A kinematic model of the pectoral fin was established based on several assumptions. Then a robotic stingray with an undulatory pectoral fin was designed and developed. Experiments were conducted to investigate the effects of various fin actuation parameters on its linear swimming velocity and the forces generated by the robotic stingray. The controllable fin parameters include oscillation frequency, wave number, maximal angular deflection of the fin rays, and the amplitude pattern of the pectoral fin. The experimental results indicate that the developed prototype is able to generate adequate thrust for self-propulsion. Linear swimming velocity and surge force increase rapidly with oscillation frequency, angular deflection, and wave number. A maximum velocity of 4.3 cm.s 1 （nearly 0.18 Body Lengths per second （BL·s-1）） and a maximum surge force of 102 mN are achieved at an oscillation frequency of 0.5 Hz, a wave number of 1, a maximum angular deflection of 30°, and an equal amplitude pattern. The sway force of the robotic fish fluctuates around 0 mN. The heave force varies with wave number and reaches its minimum at a wave number of 1.

Parametric Study of an Underwater Finned Propulsor Inspired by Bluespotted Ray

The performance ofbluespotted rays was emulated in the design ofa bioinspired underwater propulsor in the present work. First, the movement of a live bluespotted ray was captured for the swimming mode and useful information to the biomimetic mechanism design. By virtue of the modular and reconfigurable design concept, an undulatory fin propulsion prototype was developed. With a proper experimental set-up, orthogonal experiments were conducted to investigate the effect of various fin design parameters on the propulsion speed, thrust, and power of the fish robot. The controllable fin parameters include frequency, amplitude, wavelength, fin shape, and undulatory mode. The significance of these parameters was also determined by using the variance analysis. The results demonstrate that the designed propulsor, imitating bluespotted rays with large expanded undulatory fins, is able to propel itself by changing various kinematic parameters.

HYDRODYNAMIC ANALYSIS AND SIMULATION OF A SWIMMING BIONIC ROBOT TUNA

A dynamic model for undulatory locomotion was proposed to study the swimming mechanism of a developed bionic robot tuna. On the basis of inviscid hydrodynamics and rigid-body dynamics, the momentum and propulsive force required for propelling the swimming robot tuna＇s flexible body was calculated. By solving the established dynamic equations and efficiency formula, the swimming velocity and propulsive efficiency of the bionic robot tuna were obtained. The relationship between the kinematic parameters of the robot tuna＇s body curve and the hydrodynamic performances was established and discussed after hydrodynamic simulations. The results presented in this article can be used to increase the swimming speed, propulsive thrust, and the efficiency of underwater vehicles effectively.